Researchers hope waste-sniffers can combat sewer overflows

Published: September 09, 2004

Engineers at the University of Notre Dame are developing arrays of bacteria-sniffing sensors that could help cities nationwide reduce damaging overflows of raw human waste when storms swamp their antiquated sewer systems.p. Their idea, to be tested next year on the city of South Bend’s sewer system, is to pair wireless sensors with communications nodes linked to remotely activated “smart valves” that would lessen or halt overflows by closing off select sewer pipes during wet weather.p. The sensor networks the Notre Dame researchers envision could give about 800 cities nationwide now plagued by foul-smelling discharges a real-time picture of where and how much waste water is in their sewer system and allow them to better forecast overflows.p. A top goal of the $2 million project is creating technology to allow cities to fully utilize the storage potential of their sewer pipes, which can be big enough to drive a truck through.p. “Right now these cities have no way of knowing what’s where in terms of storage and when and where an overflow is going to occur. If we have these sensors down there they could tell us the real-time load of an entire sewer system,” said Jeffrey Talley, an assistant professor of civil engineering and geological sciences at Notre Dame.p. Discharges of raw sewage are a public health and environmental concern because they taint waterways with infectious pathogens and noxious waste that can cause fish kills.p. Nearly 800 older American cities and towns have so-called combined sewer systems that carry both storm runoff and sanitary waste from homes and businesses.p. When too much precipitation falls, these cities’ wastewater treatment plants are deluged with so much storm water mixed with human waste that some of it must be diverted, untreated, into rivers and streams to prevent sewers from backing up in homes and streets.p. Talley wants to hang sensor-laden instrument masts throughout these combined sewers to measure water flow and bacteria. Data relayed from these sensors would be analyzed and remotely controlled valves would open or close to turn sewer pipes into large linear storage tanks.p. Or, the water could be diverted into outdoor holding basins until wet weather subsides and the waste can be properly treated.p. Typically, sewer pipes are only partially filled with wastewater during periods of wet weather, but Talley hopes the technology can harness that unused space as storage. Sensor-lined sewers could also isolate flows with high levels of E. coli bacteria for priority treatment.p. If the system works, it could provide a relatively inexpensive fix for a costly problem affecting many of the nation’s older cities and towns.p. A survey conducted by the Environmental Protection Agency in 2000 estimated that over the next 20 years, municipalities will have to spend about $50.6 billion to reduce combined sewer overflows by 85 percent.p. Next spring, the system will get its first test when the Notre Dame researchers fit part of South Bend’s combined sewer system with about 100 sensor arrays and communication nodes that will relay data via the Internet to city officials.p. The Indiana Department of Environmental Management, which is working with more than 100 Indiana cities and towns with combined sewer systems, “would like to have a look at” the South Bend project once it’s in place, said Cyndi Wagner, chief of IDEM’s wet weather section.p. In the last few years, several Indiana communities have dug up and separated their storm and sanitary sewers. But for larger cities with mile after mile of sewer pipes, Wagner said the cost of sewer separation is prohibitive and alternatives like the Notre Dame idea could prove useful.p. The project has received a $1 million grant for Indiana’s state-funded 21st Century Research and Technology Fund, with another $1 million in matching funds expected. Its partners include Purdue University scientists and the CSO Partnership of Richmond, Va.p.